Since a cobalt-base alloy has excellent corrosion resistance and mechanical strength, it is used for a wide range of applications such as medical instruments, biomechanical materials, and wear-resistant materials. Cr, Ni, Fe, Mo, C, etc. are added in order to further improve characteristics, for example, corrosion resistance, oxidation resistance, stabilization of α-phase, and material strengthening. Various strengthening methods such as solid solution strengthening, precipitation strengthening, and work hardening methods have been proposed.
The conventional strengthening methods are based on a metallic structure in which an α-single phase or a second phase is continuously precipitated in the α-phase (Patent documents 1 and 2). Although higher strength properties are given to the Co-based alloy by precipitation of the second phase, higher strength properties have been needed in accordance with a strong demand related to use conditions, or thinner wire and miniaturization.
The strengthening method by the lamellar structure is also used for other alloy systems and a typical example thereof is a pearlite transformation which is observed in ferrous materials. When the lamellar structure of ferrite and cementite is formed by pearlite transformation, ferrous materials are highly strengthened.
As a method for strengthening the quality of materials using the lamellar structure, Cu—Mn—Al—Ni alloy having the lamellar structure disclosed in Patent document 3 is introduced by the present inventors and Co—Al binary alloy having the lamellar structure is also reported in Nonpatent document 4. Since the Co—Al alloy has the lamellar structure in which a soft α-phase and a hard β-phase are repeated and their gaps are quite small, it is used as a material of equipment capable of maintaining necessary strength even when it is made to be a thinner wire or miniaturized.    Patent Document 1: JP 7 (1995)-179967A    Patent Document 2: JP 10 (1998)-140279A    Patent Document 3: JP 5 (1993)-25568A    Nonpatent Document 4: P. Zieba, Acta mater. Vol. 46. No. 1 (1998) pp. 369-377